A key component of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
As the grains size of magnetic recording media is decreased in order to increase the areal density of the magnetic recording system, a threshold known as the superparamagnetic limit is reached for a given material and temperature. The superparamagnetic limit is a physical constraint, beyond which stable data storage is no longer feasible.
Thermal stability of magnetic recording systems can be improved by employing a recording medium formed of a material with a very high magnetic anisotropy. The energy barrier for a uniaxial magnetic grain to switch between two stabilized states is proportional to the product of the magnetic anisotropy of the magnetic material and the volume of the magnetic grains. In order to provide adequate data storage, the product of the magnetic anisotropy and volume should be as large as 60 kBT, where kB is the Boltzman constant and T is the absolute temperature, in order to provide thermally stable data storage. Although it is desirable to use magnetic materials with a high magnetic anisotropy, very few of such hard magnetic materials exist. Furthermore, with currently available magnetic materials, recording heads are not able to provide a sufficient magnetic writing field to write on such materials.
Heat assisted magnetic recording can provide a solution to this problem. In a heat assisted magnetic recording system, the magnetic medium is locally heated to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily magnetize the magnetic medium during the temporary softening of the recording medium caused by the localized heating. Heat assisted magnetic recording systems allow for the use of small grain media, which is desirable for recording at increased areal densities, with larger magnetic anisotropy at room temperature, assuring sufficient thermal stability.
Thermally assisted recording runs into problems when the available magnetic field energy becomes small with respect to the thermal energy, which leads to a high number of unrecorded grains and thus to poor quality recording. Composite medium designs have been suggested. However, the introduction of a Curie temperature (low Tc) material in conjunction with a Curie temperature (high Tc) material does not solve this problem.